The National Police Agency is considering regulating the possession of double-edged knives like the one used in Sunday's street stabbings in Tokyo's Akihabara electronics shopping district, The Yomiuri Shimbun has learned.

Currently, possessing a double-edged knife is not a crime.

The regulation under consideration would involve revising the Firearms and Swords Control Law.

Double-edged knives, which were initially developed for combat, are popular among many young Japanese. They appear in many famous Japanese video games, often wielded by the main character.

The knife allegedly used by Tomohiro Kato in Sunday's killings has a 12.5-centimeter blade.

Compared with ordinary survival knives, the double-edged knife is not suitable for practical use. The design allows for easy thrust and withdrawal, making it possible for the user to stab something many times without hurting his or her hands. In Japan, these knives can be purchased by mail.

The Firearms and Swords Control Law judges the danger of a knife by the length of its blade. The law prohibits people from carrying knives with blades of 6 centimeters or longer without a reason. Possessing these knives is allowed.

The law obliges people to obtain permission from a prefectural public safety commission to possess weapons with blades of 15 centimeters or longer. Permission is required to possess certain types of knives, including Japanese swords, spears, Japanese halberds, aikuchi (dirks without a guard) and some kinds of switchblades.

There were 4,677 illegal knife violations in 2007, an increase of 1,336 from 2002.

Many in the government are demanding that the Firearms and Swords Control Law be revised after Sunday's chilling attacks.

"We'd like to examine what we can do [to prevent recurrence of similar crimes]," National Public Commission Chairman Shinya Izumi said Tuesday.